newbie to mac and superduper!

[aus_ecl]

scenario -- HD crashes dies -- Apple replaces it with a new HD, but we use this computer for business and we do have a backup copy of all of our files etc.. on the external firewire HD, but don't know how to put them all back on our computer?

[dnanian]

All covered in the User's Guide -- "Recovering from a disaster".

In sum: start up from the backup, and use SuperDuper! to restore by copying back in the other direction. Alternatively, start the Mac with the new OS installed, and -- when prompted -- migrate from the backup.